1. Field of the Invention
The invention relates to a current control apparatus for a motor of an electric-powered vehicle, more particularly to a method and apparatus for controlling the current limit of a motor so as to conserve battery energy, to improve endurance, to avoid sudden thrusting movement of the vehicle, and to protect the motor and other power components.
2. Description of the Related Art
Due to their being environmental friendly, electric-powered vehicles are ideal for short distance travel. However, in view of current battery technology, such vehicles have unsatisfactory endurance. There is thus a need to improve motor-operating efficiency in order to improve endurance.
It has been proposed heretofore to limit the amount of current to a motor of an electric-powered vehicle to a constant value when the latter is operated in a cruise mode so as to reduce energy consumption and minimize sudden thrusting movement of the vehicle, thus enhancing consumer appeal. The constant value is usually chosen to be the rated current value of the motor to avoid damage to the motor and other power components. However, limiting the amount of current to the rated current value of the motor results in waste of energy during start-up operation of the vehicle from a stationary state.
It has also been proposed heretofore to reduce the current limit of the motor of the electric-powered vehicle when overheating of the motor and other power components occurs or when braking. However, as the current limit is still the rated current value during start-up operation of the vehicle, the aforesaid drawback persists.
Therefore, the main object of the present invention is to provide a method and apparatus for controlling the current limit of a motor so as to conserve battery energy, to improve endurance, to avoid sudden thrusting movement of the vehicle, and to protect the motor and other power components.
According to a first aspect of the invention, a method for controlling current limit of a motor of an electric-powered vehicle comprises the steps of:
setting the current limit of the motor to a smaller first value during start-up operation of the vehicle;
in response to operation of a twist-grip throttle of the vehicle to commence accelerating operation of the vehicle subsequent to the start-up operation, increasing the current limit of the motor from the smaller first value to a larger second value larger than the smaller first value in accordance with angular rotation of the twist-grip throttle from an initial position; and
when the current limit reaches the larger second value, maintaining the current limit of the motor at the larger second value in case of further operation of the twist-grip throttle from the initial position.
According to a second aspect of the invention, an apparatus for controlling current limit of a motor of an electric-powered vehicle comprises:
first means for setting the current limit of the motor to a smaller first value during start-up operation of the vehicle;
second means, in response to operation of a twist-grip throttle of the vehicle to commence accelerating operation of the vehicle subsequent to the start-up operation, for increasing the current limit of the motor from the smaller first value to a larger second value larger than the smaller first value in accordance with angular rotation of the twist-grip throttle from an initial position; and
third means, when the current limit reaches the larger second value, for maintaining the current limit of the motor at the larger second value in case of further operation of the twist-grip throttle from the initial position.
According to a third aspect of the invention, an apparatus for controlling current limit of a motor of an electric-powered vehicle comprises:
a first diode having an anode adapted to receive a first signal corresponding to a smaller first value of the current limit, and a cathode;
a first operational amplifier unit having an input adapted to receive a second signal corresponding to a larger second value of the current limit, and an output, the larger second value being larger than the smaller first value;
a second diode having a cathode coupled to the output of the first operational amplifier unit, and an anode coupled to the cathode of the first diode;
a second operational amplifier unit having an input adapted to receive a third signal corresponding to angular rotation of a twist-grip throttle of the vehicle from an initial position, and an output; and
a third diode having an anode coupled to the output of the second operational amplifier unit, and a cathode coupled to the cathode of the first diode;
the current limit of the motor being obtained from the cathode of the first diode.